The invention relates generally to a photomask, and more particularly, to a photomask for forming a contact hole in a semiconductor device.
In general, a semiconductor device has a contact structure for receiving external electrical signals. To form this contact structure, a contact hole should be formed first. The contact hole can be formed in various forms according to a kind of a semiconductor device, and in one example, can have a form in which a plurality of the contact holes is repeatedly arranged in one direction with a spacing therebetween. To form the contact hole, a photoresist layer is formed first on a target layer to be formed with the contact hole, e.g., an insulation layer. After that, a photoresist layer pattern having an opening is formed through an exposure process and a development process. Through this opening, some region of the target layer, i.e., a region in a place to be formed with the contact hole is exposed. After that, the exposed portion of the target layer is removed using this photoresist layer pattern as an etch mask to thereby form the contact hole. In this procedure, the opening provided in the photoresist layer pattern is the result of a transfer of the pattern on the photomask onto the photoresist layer through the exposure process. Accordingly, position and size of the contact hole is dependent on the pattern formed on the photomask.
FIG. 1 is a plan view illustrating an example of a prior art photomask for forming a contact hole in a semiconductor device. Also, FIG. 2 is a plan view illustrating a contact hole pattern formed using the prior art photomask of FIG. 1. Referring to FIG. 1, a prior art photomask 100 has a structure in that a light shielding layer 110 such as a chromium (Cr) layer is disposed on a light transmitting substrate not shown). The light shielding layer pattern 110 exposes some portion of a surface of the light transmitting substrate and this exposed portion is a transfer pattern 120 corresponding to the contact hole to be formed. This transfer pattern 120 is disposed in plural along a transverse direction with a predetermined spacing. Referring to FIG. 2, as the result of implementing exposure and development on the photoresist layer using the photomask the photoresist layer 210 remains in a region corresponding to the light shielding layer pattern 110, and a prior art contact hole pattern 220 is formed in a region corresponding to the transfer pattern 120. However, as the degree of integration of semiconductor device has increased, a size of the contact hole to be formed and a gap between the contact holes become smaller and smaller. Therefore, there is often generated a bridge in that the formed prior at contact hole pattern 220 is connected with an adjacent prior art contact hole pattern 220. Accordingly the prior art contact hole patterns have recently been arranged in a zigzag form to restrict the generation of the bridge.
FIG. 3 is a plan view illustrating an example of a prior art photomask in zigzag form for forming a contact hole. Also, FIG. 4 is a plan view illustrating a prior art contact hole pattern formed using the prior art photomask of FIG. 3. Referring to FIG. 3, in the prior art photomask 300, the light shielding layer pattern 310 is disposed on the light transmitting substrate (not shown) to define the transfer pattern 320 corresponding to the contact hole to be formed. This transfer pattern 320 is a region in which the light transmitting substrate is exposed, and is arranged in a zigzag form. Referring to FIG. 4, as the result of implementing exposure and development on the photoresist layer using the prior art photomask 300, the photoresist layer 410 remains in a region corresponding to the light shielding layer pattern 310, and a prior art contact hole pattern 420 having a zigzag form like the transfer pattern 320 is formed in a region corresponding to the transfer pattern 320.
However, when forming the prior art contact hole pattern 420 in a zigag form the possibility of bridge generation is lowered but it is difficult to adjust depth of focus (DOF) upon the exposure. Accordingly, recently attempts have tried enhancing the depth of focus by inserting an auxiliary pattern (not shown) in the transfer pattern 320 of the prior art photomask 300. However, it is still difficult to maintain the spacing a (a FIG. 4) between the adjacent prior art contact hole patterns 420 to a predetermined spacing, and there occurs a problem that a length (b of FIG. 4) from the lowermost to the uppermost of the prior art contact hole tterns 429 exceeds a limit length defined upon design.